You know, I'd be willing to bet that the problem some of you are having with prunes isn't really the prunes themselves but mold that grows on/in them.

That's a very interesting point. If that's the case, how could one get rid of the mold? I've recently found some prunes that don't need presoaking and have no additives/preservatives, but I'm wondering whether they might have that very same problem...

I presoak them overnight, in plenty of filtered water. †I actually change the water I soak them in a few times. †Also when I start cooking them I follow the advice of an ayurvedic cookery book I've got and I boil them for a few minutes, throw the water away and replace it with fresh water and carry on cooking them for the necessary time.

I've never seen kombu seaweed around.

It appears that you are presoaking and cooking your beans correctly. Adding the kombu may help.